Change file_magic structure contents

Move header_size field to the end of the structure, so that other
programs can still tell it is a sysstat sar data file, even though
the format has changed.

Also, to avoid causing format changes, add padding to the file_magic
structure so that when they grow in size other tools can still
handle the existing data.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>

diff --git a/sa.h b/sa.h
index 1ef74133b30ad1f9b496dcd3405f7d42c17d7884..532170c94897a14630b306edfd7429a5145d7594 100644 (file)
--- a/sa.h
+++ b/sa.h
@@ -487,10 +487,6 @@ struct activity {
 
 /* Structure for file magic header data */
 struct file_magic {
-       /*
-        * Size of file's header (size of file_header structure used by file).
-        */
-       unsigned int header_size;
        /*
         * This field identifies the file as a file created by sysstat.
         */
@@ -506,6 +502,14 @@ struct file_magic {
        unsigned char  sysstat_patchlevel;
        unsigned char  sysstat_sublevel;
        unsigned char  sysstat_extraversion;
+       /*
+        * Size of file's header (size of file_header structure used by file).
+        */
+       unsigned int header_size;
+       /*
+        * Padding. Reserved for future use while avoiding a format change.
+        */
+       unsigned char pad[64];
 };
 
 #define FILE_MAGIC_SIZE        (sizeof(struct file_magic))